Integrated Services Digital Network u Public networks are

Integrated Services Digital Network u Public networks are used for a variety of services – Public Switched Telephone Network – Private Lines (leased) – Packet Switched Data Networks – Circuit Switched Data networks 1

ISDN u Users have a variety of equipment to connect to public networks – Telephones – Private Branch Exchanges – Computer Terminals or PCs – Mainframe Computers u. A variety of physical interfaces and access procedures are required for connection 2

ISDN u The telephone network has evolved into a digital one with digital exchanges and links u The signalling system has become a digital message-oriented common channel signalling system (SS#7) u The term ‘Integrated Digital Network’ is used to describe these developments 3

ISDN u The Public Switched Telephone network is still analogue from the subscriber to the local exchange u The need has arisen to extend the digital network out to subscribers and to provide a single standardised interface to all different users of public networks u ISDN fulfils that need 4

Figure 15 -1 WCB/Mc. Graw-Hill ISDN Services The Mc. Graw-Hill Companies, Inc. , 1998

Integrated Services Digital Network Packet switched network Telephone Circuit switched network Data terminal PBX Alarm LAN Customer ISDN Interface ISDN central office ‘Digital pipe’ Databases Other Networks & services 6

Figure 15 -4 Analog and Digital Services WCB/Mc. Graw-Hill The Mc. Graw-Hill Companies, Inc. , 1998

Figure 15 -5 Integrated Digital Network WCB/Mc. Graw-Hill The Mc. Graw-Hill Companies, Inc. , 1998

Figure 15 -6 Integrated Services Digital Network WCB/Mc. Graw-Hill The Mc. Graw-Hill Companies, Inc. , 1998

ISDN u In Practice there are multiple networks providing the service nationally u The user however, sees a single network 10

Benefits to Subscribers u Single access line for all services u Ability to tailor service purchased to suit needs u Competition among equipment vendors due to standards u Availability of competitive service providers 11

Architecture Integrated Digital Network Common physical interface ISDN central office Digital circuitswitched backbone Packet-switched network ISDN subscriber loop Basic 2 B+D Primary 30 B+D Network-based processing services 12

ISDN Channels u The Digital pipe is made up of channels one of three types u B channel, D channel or H channel u Channels are grouped and offered as a package to users 13

B Channel B channel-64 kbps u B is basic user channel u – can carry digital data or PCM-encoded voice – or mixture of lower rate traffic. 14

B Channel u Four kinds of connection possible u Circuit-switched u Packet-switched - X. 25 u Frame mode - frame relay (LAPF) u Semipermanent - equivalent to a leased line 15

D Channel u. D Channel - 16 or 64 kbps u Carries signalling information to control circuit-switched calls on B channels u Can also be used for packet switching or low-speed telemetry 16

H Channel u Carry user information at higher bit rates 384 kbps or 1536 kbps or 1920 kbps u Can be used as a high-speed trunk u Can also be subdivided as per user’s own TDM scheme u Uses include high speed data, fast facsimile, video, high-quality audio 17

ISDN Channels and their Applications 18

ISDN Channel Groupings u Basic Access Õ two 64 kbps B channels Õ plus one 16 kbps D channel u B channels can be used for voice and data u simultaneous calls to separate destinations supported u D channel used for signalling and also for data using X. 25 19

ISDN Basic Access u Intended for small business and residential use u A single physical interface is provided u Data rate is 144 kbps plus 48 kbps overhead bits totalling 192 kbps u Most existing subscriber loops can support basic access 20

Figure 15 -7 Basic Rate Interface WCB/Mc. Graw-Hill The Mc. Graw-Hill Companies, Inc. , 1998

Figure 15 -17 WCB/Mc. Graw-Hill BRI Frame The Mc. Graw-Hill Companies, Inc. , 1998

ISDN Primary Access u Intended for users with greater capacity requirements u Example would be a digital PBX u Two standards exist – 1. 544 Mbps American – 2. 048 Mbps European 23

Figure 15 -20 WCB/Mc. Graw-Hill PRI Frame The Mc. Graw-Hill Companies, Inc. , 1998

Figure 15 -8 WCB/Mc. Graw-Hill Primary Rate Interface The Mc. Graw-Hill Companies, Inc. , 1998

ISDN Primary Access u Typically it is structured as 30 B channels plus one 64 kbps D channel (Europe) u Can also be structured as H channels – 5 H 0 +D for a 2. 048 Mbps interface – or 1 H 12 +D 26

ISDN Primary Interface u Multiple channels multiplexed on single medium u Only point to point configuration is allowed u Typically supports a digital PBX and provides a synchronous TDM facility 27

User Access u Defined using two concepts – Functional groupings of equipment – Reference points to separate functional groupings 28

Typical User Access Layout ISDN NT Tele phone 2 -wire Subscriber Loop 4 -wire S-bus PC with ISDN Interface Card Integrated Voice/data Terminal User/network Interface Up to 8 devices point to multi-point mode 29

Figure 15 -9 Functional Grouping WCB/Mc. Graw-Hill The Mc. Graw-Hill Companies, Inc. , 1998

Figure 15 -10 Reference Points WCB/Mc. Graw-Hill The Mc. Graw-Hill Companies, Inc. , 1998

ISDN Protocol Architecture Application Presentation Session End-end user signalling Transport Network I. 451/Q. 931 X. 25 for further call control packet level study Datalink LAPD (Q 921) Physical X. 25 packet level Frame Relay LAPB I. 430 basic interface + I. 431 primary interface 32

Figure 15 -12 ISDN Layers for B and D Channels WCB/Mc. Graw-Hill The Mc. Graw-Hill Companies, Inc. , 1998

ISDN Data Link Layer u Link Access Protocol for the D channel (LAPD) defined for ISDN u Three applications are supported – Control Signalling – Packet Switching – Telemetry 34

B-Channel u Uses – Circuit Switching – Semi-permanent circuits – Packet switching 35

B-Channel u Circuit Switching – Circuit is set up on B-channel on demand – D-channel call control protocol is used – Transparent full-duplex digital data path established between users – Layers 2 to 7 are not visible to ISDN or specified 36

B-Channel u Semipermanent circuit can be set up by prior agreement between users and network operator u Can be for indefinite time or at specified times during day or week u As with circuit switched connection, full duplex digital data path is established u Layers 2 to 7 are not visible to ISDN or specified 37

D-Channel Packet Switching u Integrated X. 25 service can be accessed by D-Channel in addition to B-Channel u ISDN provides a semi-permanent connection to a packet switching node within ISDN u The X. 25 level 3 protocol is used for the packet layer u LAPD is used for the link layer 38